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I purchased this rock at a garage sale. I believe the person told me it was mexican opal, but I think it might be amethyst? It is 8" wide, 6" deep and 4" high. It weighs about 4 lbs. I don't know enough about rocks but I think I saw a raw amethyst rock that is similar. I probably overpayed at $35 so I would like to know more about it. Thanks folks! - Kari

Okay...I asked Tim at 'Cigar Box Rocks' and he said it is probably..."Tiffany stone. That is a slang work for Bertrandite.
The best way I can describe it is a type of Opalized Fluorite." I think this makes it much more valuable now. $35 does not sound like so much now.

Well, it definitely doesn't look like opal or amethyst. Try scratching it with a knife and if it scratches, that will rule out amethyst. It looks most like fluorite. It is too purple to be sodalite, though the variety hackmanite can be purple. Does it fluoresce at all?